How Many Volts Will Stop a Human Heart? Understanding Electricity and the Human Body

Electricity is a powerful force — one that can be both useful and dangerous. While we use it every day for lighting, heating, and powering devices, even a small amount of electric current passing through the human body can be fatal. One of the most common questions people ask is, “How many volts does it take to stop a human heart?”

The answer isn’t as simple as a single number, because voltage alone doesn’t determine the danger. The real risk depends on several factors, including the current (amperage), the path electricity takes through the body, the duration of contact, and the person’s overall health. Our team of certified low voltage experts in Los Angeles emphasizes the importance of safety when handling any electrical current, no matter how small.

Voltage vs. Current: What Actually Causes Harm

Many people assume it’s the voltage that kills, but it’s actually the current (measured in amperes, or amps) that causes fatal damage. Voltage is the electrical force that pushes current through a conductor — including your body — while current is what does the real harm.

Even a small amount of current, as little as 100 milliamperes (0.1 amps), can trigger ventricular fibrillation, a chaotic and deadly heart rhythm that stops effective blood circulation.

So, while voltage is what drives the current, it’s the current that stops the heart.

How Many Volts Can Be Deadly?

The human body’s resistance to electricity varies depending on moisture, skin condition, and contact area.

Here’s a general breakdown:

Dry skin: 100,000 ohms of resistance (approximate)
Wet skin: 1,000 ohms or less

According to Ohm’s Law (V = I × R), a voltage of around 100 volts across wet skin can push 100 milliamperes (0.1 amps) of current — enough to stop the heart.

That means under certain conditions, even household voltages (120V or 240V) can be fatal, especially if the skin is damp or if the shock passes through the chest.

Factors That Affect Electrical Injury

Several factors determine how electricity affects the body:

Path of the current: A shock passing from one hand to the other or from hand to foot can travel through the heart.
Duration of contact: The longer you’re exposed, the more dangerous it becomes.
Voltage and current: Higher voltage increases the chance of current overcoming the body’s resistance.
Type of current: Alternating current (AC) — like that from household outlets — is more likely to cause heart fibrillation than direct current (DC).
Environment: Wet or humid conditions drastically lower skin resistance.

Even a small shock in the right (or wrong) conditions can be lethal.

Real-World Examples

Household electricity (120V/240V): Potentially fatal under wet or prolonged contact conditions.
Car batteries (12V DC): Usually not deadly unless the skin is broken or wet — too little voltage to overcome body resistance.
High-voltage lines (10,000V+): Almost always fatal due to tissue burns, nerve damage, and cardiac arrest.

This is why electricians, linemen, and other professionals use strict safety gear and grounding systems when working with live circuits.

How Electric Shock Affects the Heart

Electric current interferes with the heart’s electrical signals. If current passes through the chest, it can disrupt the normal rhythm and cause:

Ventricular fibrillation (VF): Rapid, erratic heartbeat that prevents blood flow.
Asystole: Complete cardiac arrest (no heartbeat).
Muscle contractions: Can “freeze” someone to a live circuit, prolonging contact.

Immediate CPR and defibrillation can sometimes restore a heartbeat, but survival depends heavily on how quickly help arrives. Even systems with lower current can pose risks under certain conditions. Learn more in our post, can you get shocked from low voltage lighting.

How to Stay Safe Around Electricity

You can’t always see or hear electricity, but a few precautions go a long way:

Never touch electrical devices with wet hands.
Avoid using electrical equipment near water.
Always switch off breakers before working on wiring.
Use insulated tools and protective gloves when handling electrical components.
Call a licensed electrician for repairs or installations.

Even “low voltage” circuits can be dangerous in the wrong circumstances.

Medical Help After an Electric Shock

If someone suffers an electrical shock — even if they seem fine — seek medical attention immediately. Internal injuries such as heart rhythm disturbances or muscle damage might not be visible right away.

Call 911 if the person:

Loses consciousness
Has visible burns
Is experiencing chest pain or irregular heartbeat
Shows difficulty breathing or confusion

Prompt medical evaluation can save lives.

The Bottom Line

There’s no exact “voltage number” that stops a human heart, because the danger depends on current, duration, and conditions. However, as little as 100 volts can be lethal if it drives enough current through the heart. Working with electrical systems requires proper precautions. Check out the essential safety equipment used for low voltage circuits to minimize risk.

Always treat electricity with respect. Whether at home or at work, follow safety protocols, use protective gear, and never underestimate the power of electrical energy.